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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011 
estimate actual Gray Trembler egg size because 
egg mass (and, thus, egg size) correlates with 
adult body mass in passerines (Martin et al. 2006). 
However, to our knowledge, the Gray Trembler 
egg dimensions we present represent the only 
available for the species and offer a basis for 
comparison with any egg dimension data col¬ 
lected for Gray Tremblers in the future. 
Our description of the Gray Trembler’s nest 
stresses the importance of accurate data for 
conservation efforts. The similarity in physical 
appearance of the observed nest and eggs of the 
Gray Trembler on St. Lucia, a species of least 
concern (BirdLifelnternalional 2009). to the nests 
and eggs of its endangered relative, the White¬ 
breasted Thrasher, suggests nests containing eggs 
cannot be attributed to one or the other of these 
species without identifying the birds attending 
the nest. 
The Gray Trembler is not presently considered 
at risk, but it experiences similar extrinsic and 
intrinsic conditions as other species restricted to 
islands. Island endemics, compared with species 
having continental ranges, comprise a dispropor¬ 
tionately large percentage of threatened and 
endangered avifauna (Temple 1985). Gathering 
basic natural history data for the trembler and 
other poorly known species can inform manage¬ 
ment and help avert conservation problems. For 
example, the White-breasted Thrasher was re¬ 
cently discovered to be a facultative cooperative 
breeder with three or more individuals contribut¬ 
ing care at many nests (Temple et al. 2006). This 
social system, which is well known in several 
other mimids (e.g., Galapagos mockingbirds, 
Nesomimus spp.; Curry and Grant 1990), can 
strongly influence effective population size and 
population persistence. Whether helpers are 
present at Cinclocerthia nests remains unknown. 
We hope the accurate, unequivocal nest and egg 
descriptions provided here will facilitate future 
study and clarify details of the Gray Trembler's 
natural history. 
ACKNOWLEDGMENTS 
We ihunk Stephen Lesmond for invaluable assistance in 
the field. M. N. Morton for field logistics. Design 
Construction Group and St. Lucia Forestry Department 
for research permission and additional logistical assistance, 
and the staff of the Hwell Sale Stewart Library at the 
Academy of Natural Sciences of Philadelphia for assis¬ 
tance. Funding tor field studies on St. Lucia was provided 
by the Society for Integrative and Comparative Biology 
Cooper Ornithological Society, Wilson Ornithological 
Society, Association of Field Ornithologists, Philadelphia 
Zoo. Sigma Xi. and Villanova University Graduate School. 
We thank M. L. Cody. A. R. Keith, and R. L. Zusi for 
offering insight on the accuracy of original Gray Trembler 
nest descriptions, Daniel Hanley for providing useful 
references, and Avni Malhotra, R. Roy Johnson, an 
anonymous reviewer, C. E. Braun, and Julian Kapoor for 
comments that improved the manuscript. 
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